1. Field of the Invention
This invention is directed toward artificial lift systems used to produce fluids from boreholes such as oil and gas wells. More particularly, the invention is directed toward apparatus and methods for measuring dimensions and flaws in coiled sucker rod as the rod string is removed from or inserted into the borehole.
2. Background of the Art
Oil and gas wells are typically drilled with a rotary drill bit and a circulating drilling fluid or xe2x80x9cmudxe2x80x9d system. Subsequent to the drilling of a well, or alternately at intermediate periods during the drilling process, the borehole is cased typically with steel casing, and the annulus between the borehole and the outer surface of the casing is filled with cement. The casing preserves the integrity of the borehole by preventing collapse or cave-in. The cement annulus hydraulically isolates formation zones penetrated by the borehole that are at different internal formation pressures. Producing zones are typically produced through tubing suspended within the casing.
Fluids can be produced from oil and gas wells by utilizing internal pressure within a producing zone to lift the fluid through the well borehole to the surface of the earth. If internal formation pressure is insufficient, artificial fluid lift means and methods must be used to transfer fluids from the producing zone and through the borehole to the surface of the earth.
The most common artificial lift technology utilized in the domestic oil industry is the sucker rod pumping system. A sucker rod pumping system consists of a pumping unit that converts a rotary motion of a drive motor to a reciprocating motion of an artificial lift pump. A pump unit is connected to a polish rod and a sucker rod xe2x80x9cstringxe2x80x9d which, in turn, operationally connects to a rod pump in the borehole. The string can consist of a group of connected, essentially rigid, steel sucker rods sections (commonly referred to as xe2x80x9cjointsxe2x80x9d) in lengths of 25 or 30 feet (ft), and in diameters ranging from ⅝ inches (in.) to 1xc2xc in. Joints are sequentially connected or disconnected as the string is inserted or removed from the borehole, respectively. Alternately, a continuous sucker rod in diameters ranging from xc2xe inches (in.) to 1xc2xc in. (hereafter referred to as COROD) string can be used to operationally connect the pump unit at the surface of the earth to the rod pump positioned within the borehole. A delivery mechanism rig (hereafter CORIG or any injector) is used to convey the COROD string into and out of the borehole.
A prior art borehole pump assembly of a sucker rod operated artificial lift systems typically utilizes a progressing cavity pump (hereafter PCP) positioned within wellbore tubing. The PCP consists of a rotor operating within a stator, and is positioned at or near a formation to be produced. The sucker rod string is rotated from surface of the earth by a rotary well head drive, thereby imparting rotation to the rotor element of the PCP to provide desired fluid lifting. This system has proven to be an effective means of lifting primary heavy oil formations where sand is suspended within the produced fluid. As the sand laden oil mixture rises in the tubing string, the fluid acts like abrasive slurry that abrades the sucker rod string. This abrasion can be general over a length of the rod thereby altering the cross section area of the rod string over an extended length. Abrasion can be localized to form a groove or a ring around a limited vertical extent of the sucker rod string. Significant abrasive wear can lead to mechanical failure of the rod. In addition, produced fluids are often corrosive. These corrosive fluids can attack the sucker rod surface causing pitting that may lead to fatigue cracking and subsequent rod failure.
To summarize, fluids produced with a PCP operated with a COROD sucker rod system can adversely alter the sucker rod string. The fluid can abrade the sucker rod string over an extended length thereby reducing cross sectional area of the string. The fluid can xe2x80x9cincisexe2x80x9d groves or rings in vertically localized sections of the rod string thereby forming localized flaws. Corrosive fluid can pit or otherwise distort virtually any portion of the rod string that it contacts. All of these alterations can adversely affect the physical integrity of the sucker rod string that can lead to costly system failures. From an economic, operational and safety viewpoint, it is of prime importance to monitor the sucker rod for all types of alterations so that proper remedial action can be taken. More specifically, it is desirable to monitor sucker rod for alterations as the string is being removed from or inserted into the well borehole.
Electromagnetic Inspection (EMI) systems as well as eddy current surface inspection systems have been used to detect incised type flaws in sucker rod during manufacture and also during field use. Linear transducers have been used to measure sucker rod cross sectional dimensions, thereby providing a means of detecting wear type alteration of rod dimensions over extended lengths. These measurements have been limited to conventional sucker rod joints in the prior art. ICO Shearer (http:// www.icoshearerinc.com) offers an inspection service for continuous sucker rods. An inspection head assembly is used which will allow a 2 in. diameter rod which is pined and coupled to pass there through. This service is performed while the rod string is being removed from a well borehole. These prior art systems are, however, not practical for monitoring the condition of a conventional sucker rod string in xe2x80x9creal-timexe2x80x9d as it is pulled from or inserted into a well borehole.
Eddy current systems are very effective for at detecting surface defects such as cracks, grooves, gouges and the like. EMI systems have been used to detect localized defects or flaws in sucker rods. All of these systems require that a magnetic flux be induced within the rod. Surface defects result in magnetic flux leakage. Sensors measure the leakage and are thereby used to locate and even quantify the surface defect. An EMI system has been used to detect localized flaws in joints of tubulars, wherein the system employs Hall effect transducers and an energized coil that induces the magnetic flux within the tubular. Again, these measurements have been limited to inspecting the body of conventional sucker rod joints in the prior art, and are therefore are not practical for monitoring the condition of a conventional sucker rod string as it is pulled from or inserted into a well borehole. This limitation is partly due to forged pins at each end of a conventional sucker rod joint, and the non-consistent speed at which a rig crew pulls a conventional sucker rod string from a well borehole.
Several prior art systems are available for the inspection of continuous sections of wire rope. As examples, inspection systems wire rope inspection systems are disclosed in publications and several U.S. Patents to Noranda. An inspection system is offered by NDTech (http:///www.ndtettech.com/ndtbro.pdf). Prior art wire rope inspection systems are summarized in the publication xe2x80x9cInspection of Wire Ropes in Service: A Critical reviewxe2x80x9d, Frank A. Iddings and G. P. Singh, Materials Evaluation, Vol. 43, No. 13, pp. 1592-1605 (1985). The systems are typically portable, use permanent magnets to create a magnetic flux within the rope section being inspected, and all use the measure of magnetic flux leakage for flaw detection. Some systems measure the total magnetic flux to determine the effective cross-sectional area of the wire rope. This measurement is based upon the principle that for a saturated ferromagnetic rope, the magnetic flux is proportional to the cross-sectional area of the rope. A measure of magnetic flux can, therefore, be used to calculate the cross sectional area of the rope. Although not suitable for conventional sucker rod strings comprising joints, this technique can be adapted to measure the cross sectional area of continuous sucker rod strings, namely COROD strings, as the string is conveyed within a well borehole. It should be noted that a typical COROD string does not necessarily wear or abrade evenly over an extended length, thus the cross section can be oval or some shape other than round. In order to increase accuracy of cross sectional area measurements using linear systems on round rod, at least two measurements should be taken at ninety degrees and averaged. Computing cross sectional area from a measure of magnetic flux is, therefore, equivalent to, or even superior in accuracy to averaging multiple linear diameter measurements to calculate area.
Typically, all rod tests are related to operating stress levels such as yield stress, ultimate stress, and fatigue stress levels. Stress is defined as applied load divided by the cross sectional area of the rod. Cross sectional area, if measured directly with at least a 0.5% to 1.0% accuracy, is a much better indicator of rod condition that a cross sectional area computed from linear dimensions. If the rod is worn asymmetrically, cross sectional area computed from two linear dimensions taken at 90 degrees to each other will have significant error if the cross section is assumed to be circular. Prior art systems, including the Shearer system, measure rod dimensions using linear transducers. These dimensional measurements are subsequently used to compute cross sectional area of the rod which, as discussed above, can be in error if wear is oval.
Application for Canadian Patent No. 2,166,953 discloses apparatus and methods for measuring gross sectional area of wire rope by saturating a section of wire rope and subsequently determining the gross section from a measure of flux leakage. Furthermore apparatus and methods are disclosed for measuring geometry of flaws in wire rope using responses of Hall effect detectors. The reference does not teach the measurement of cross sectional area and flaws of continuous sucker rod, and does not teach the generation of real time reports of such measurements as a function of position along the continuous sucker rod.
The present invention is a system for measuring and recording dimensions and flaws in COROD as the sucker rod string is removed from or inserted into a borehole by means of a CORIG or other type of continuous rod handling injector.
COROD is passed through a sensor unit at the surface of the earth. The sensor unit is preferably attached to the CORIG, but can be located elsewhere as long as it is positioned between the head of the well and the service or transport reel receiving and coiling the COROD string. The sensor unit contains a magnet that saturates an increment of COROD within the sensor unit. The magnet is preferably a permanent magnet, but can alternately be an electromagnet. A coil within the sensor unit surrounds the COROD, and is used to measure magnetic flux induced within the COROD increment passing through the sensor unit. This measurement is used to compute cross sectional area of the COROD increment. One or more Hall effect transducers and sector coils are positioned within the sensor unit in the immediate vicinity of the COROD increment. Responses of the preferably multiple Hall effect transducers and sector coils are used to measure flux leakage. These measurements are, in turn, used to detect and to quantify localized flaws in the COROD such as grooves, gouges, pits and the like. It is again emphasized that the measurement is essentially continuous as the COROD string moves up and down within the sensor unit.
A depth measuring device cooperates with the COROD and CORIG or other type of continuous rod handling injector to determine the position of the increment of rod being measured with respect to a reference point, such as the downhole terminus of the COROD string. Magnetic flux measurements, Hall effect transducer and sector coils measurements, and depth measurements are input into a processor unit which contains a clock, an analyzer and a central processing unit (CPU). Magnetic flux is converted to cross sectional area of the COROD by means of the CPU using a predetermined calibration factor. Hall effect transducer and sector coils responses are combined with the clock output and depth measuring device response to obtain transducer responses as a function of position along the increment of rod being measured. These responses as a function of position are processed by an analyzer to determine (a) if a flaw is present, and (b) the type of flaw or flaw xe2x80x9cgeometryxe2x80x9d. Flaw geometry is determined from the xe2x80x9cshapexe2x80x9d of the transducer response as a function of position along the increment of rod being measured. The output from the depth measuring device is also input into the CPU. The CPU produces a tabulation or xe2x80x9clogxe2x80x9d of COROD cross sectional area, and a physical description or map of any COROD flaws as a function of position along the COROD string. This allows any mechanical COROD problems to be detected, located and quantified as the continuous sucker rod string is being conveyed within the well. Appropriate remedial actions can then be taken based upon the severity of the detected and quantified problem.
The system has a cross sectional area accuracy of about 0.5%. As an example, a round rod with a diameter of 1.000 in. which exhibits a measured 0.5% reduction in cross sectional area due to wear correspondingly exhibits a measurable 00025 in. reduction in diameter dimension. Vertical length measurements are made in increments of 0.25 in. with a location accuracy on the COROD string of about 12 in. This specification is significantly variably depending upon hardware and electronics of the system, and can be made more accurate if required. As an example, using a vertical length measuring wheel with a diameter of 11.853 in. and an encoder generating 2,048 encoder pulses per revolution of the measuring wheel, a linear measurement of 0.018 in. per encoder pulse is obtained. Combinations of wheel diameter and encoder sensitivity can be combined to obtain virtually any linear resolution required by a particular application of the system. Expectations are that flaws of about 0.015 in. wide or wider, and about 0.015 in. deep or deeper can be detected. Rod dimensions for round rod are computed from cross sectional area measurements.
The generated log typically indicates the time that each measured flaw is measured, the position and length dimensions of the flaw relative to the reference point on the COROD string, and the direction of rod movement when sampling occurs. The system also provides a real time calculated dimensional display of the COROD, and the current COROD cross sectional area as a function of length position.
The system is easily adapted to, installed on, and removed from existing CORIGS, can operate with COROD ranging in diameter from 0.750 in. to 1.25 in., and can operate at a CORIG gripper speeds of up to about 120 feet per minute.
Logged data is available at the well site in an Excel importable file, a hard copy graph, or an electronic file such as a disk. The system also has a visible, real time adjustable Go/No-Go limit indicator so that the GORIG can be immediately stopped if the sensed COROD condition fails to meet predetermined standards. The system is capable of operating at temperatures as low as xe2x88x9230 degrees Centigrade.
A DOS, Windows, Linux or other real time operating system based personal computer (PC) or industrial computer configured as a laptop system or a rack mounted system can be configured to serve as the system processor unit. The processor unit can be located as far away as 200 feet from the sensor unit, can be connected to the sensor unit by a wireless or hard wire link, and can be operated by a field rig crew.